Alkaline cell with improved cathode

ABSTRACT

An alkaline cell having an anode comprising zinc, an aqueous alkaline electrolyte, a cathode mixture comprising cathode active material comprising copper oxide or copper hydroxide. Graphitic carbon, preferably expanded graphite or graphitic carbon nanofibers are added to the cathode mixture thereby resulting in a sharp drop in cathode resistivity. The cathode active material preferably comprises between about 80 and 92 percent by weight of the cathode. The sharp drop in cathode resistivity resulting from the addition of expanded graphite or graphitic carbon nanofibers makes the cell suitable for use as a primary alkaline cell having good capacity. The graphitic carbon, preferably graphitic nanofibers comprise preferably between about 4 and 10 percent by weight of the cathode. The carbon nanofibers have an average diameter desirably less than 500 nanometers, preferably between about 50 and 300 nanometers.

FIELD OF THE INVENTION

This invention relates to an aqueous alkaline cell with a cathodecomprising copper oxide or copper hydroxide, particularly such cathodeswith a conductive additive of expanded graphite or graphitic carbonnanofibers.

BACKGROUND OF THE INVENTION

Conventional alkaline electrochemical cells have an anode comprisingzinc and a cathode comprising manganese dioxide. The cell is typicallyformed of a cylindrical casing. The casing is initially formed with anenlarged open end and opposing closed end. After the cell contents aresupplied, an end cap with insulating plug is inserted into the open end.The cell is closed by crimping the casing edge over an edge of theinsulating plug and radially compressing the casing around theinsulating plug to provide a tight seal. A portion of the cell casing atthe closed end forms the positive terminal.

Primary alkaline electrochemical cells typically include a zinc anodeactive material, an alkaline electrolyte, a manganese dioxide cathodeactive material, and an electrolyte permeable separator film, typicallyof cellulose or cellulosic and polyvinylalcohol fibers. The anode activematerial can include for example, zinc particles admixed withconventional gelling agents, such as sodium carboxymethyl cellulose orthe sodium salt of an acrylic acid copolymer, and an electrolyte. Thegelling agent serves to suspend the zinc particles and to maintain themin contact with one another. Typically, a conductive metal nail insertedinto the anode active material serves as the anode current collector,which is electrically connected to the negative terminal end cap. Theelectrolyte can be an aqueous solution of an alkali metal hydroxide forexample, potassium hydroxide, sodium hydroxide or lithium hydroxide. Thecathode typically includes particulate manganese dioxide as theelectrochemically active material admixed with an electricallyconductive additive, typically graphite material, to enhance electricalconductivity. Optionally, small amount of polymeric binders, for examplepolyethylene binder and other additives, such as titanium-containingcompounds can be added to the cathode.

The manganese dioxide used in the cathode is preferably electrolyticmanganese dioxide (EMD) which is made by direct electrolysis of a bathof manganese sulfate and sulfuric acid. The EMD is desirable since ithas a high density and high purity. The electrical conductivity(resistivity) of EMD is fairly low. An electrically conductive materialis added to the cathode mixture to improve the electric conductivitybetween individual manganese dioxide particles. Such electricallyconductive additive also improves electric conductivity between themanganese dioxide particles and the cell housing, which also serves ascathode current collector. Suitable electrically conductive additivescan include, for example, conductive carbon powders, such as carbonblacks, including acetylene blacks, flaky crystalline natural graphite,flaky crystalline synthetic graphite, including expanded or exfoliatedgraphite. The resistivity of graphites such as flaky natural or expandedgraphites can typically be between about 3×10⁻³ ohm-cm and 4×10⁻³ohm-cm.

It is desirable for a primary alkaline battery to have a high dischargecapacity (i.e., long service life). Since commercial cell sizes havebeen fixed, it is known that the useful service life of a cell can beenhanced by packing greater amounts of the electrode active materialsinto the cell. However, such approach has practical limitations such as,for example, if the electrode active material is packed too densely inthe cell, the rates of electrochemical reactions during cell dischargecan be reduced, in turn reducing service life. Other deleterious effectssuch as cell polarization can occur as well. Polarization limits themobility of ions within both the electrolyte and the electrodes, whichin turn degrades cell performance and service life. Although the amountof active material included in the cathode typically can be increased bydecreasing the amount of non-electrochemically active materials such aspolymeric binder or conductive additive, a sufficient quantity ofconductive additive must be maintained to ensure an adequate level ofbulk conductivity in the cathode. Thus, the total active cathodematerial is effectively limited by the amount of conductive additiverequired to provide an adequate level of conductivity.

Although such alkaline cells are in widespread commercial use there is aneed to improve the cell or develop a new type of cell that is costeffective and exhibits reliable performance as well as high capacity(mAmp-hours) and high service life for normal applications such asflashlight, radio, and portable CD players.

SUMMARY OF THE INVENTION

An aspect of the invention is directed to a primary (nonrechargeable)electrochemical alkaline cell having an anode comprising zinc and acathode mixture comprising copper oxide (CuO) or copper hydroxide(Cu(OH)₂) cathode active material. If copper oxide is employed in thecathode mixture, its purity is desirably at least 97, preferably atleast 99 percent by weight, desirably between about 97 and 99.8 percentby weight, e.g. about 99.5 percent by weight. A graphitic carbon isadded to the cathode mixture. It has been determined that a graphiticcarbon comprising expanded graphite or graphitic carbon nanofibers ormixtures thereof provides a very suitable conductive additive. Suchgraphitic carbon material significantly reduces the cathode resistance,elevates the cell's running voltage and increases cell capacity andperformance. The addition of graphitic carbon nanofibers to cathodescomprising copper oxide or copper hydroxide is particularly desirable.The conductive material thus is desirably composed essentially entirelyof expanded graphite or graphitic carbon nanofibers or mixtures thereof.Preferably, the cathode mixture comprises between about 3 and 10 percentby weight, preferably between 4 and 10 percent by weight of thegraphitic carbon nanofibers. Preferably, the graphitic carbon nanofibershave a mean average diameter less than 500 nanometer, more preferablyless than 300 nanometers. Desirably the graphitic carbon nanofibers havea mean average diameter between about 50 and 300 nanometers, typicallybetween about 50 and 250 nanometers.

The anode and cathode include an aqueous alkaline solution, preferablyaqueous KOH solution. The cathode desirably comprises between about 4and 10 percent by weight of the conductive additive. The copper oxide ispreferably in the form of a powder having an average particle sizebetween about 1 and 100 micron. The cathode mixture includes an aqueousKOH solution, desirably having a concentration of between about 30 and40 percent by weight, preferably between 35 and 45 percent weight KOH inwater. The aqueous KOH solution desirably comprises between about 5 and10 percent by weight of the cathode mixture. The cathode active materialcomprising copper oxide or copper hydroxide, preferably comprisesbetween about 80 and 92 percent by weight of the cathode mixture.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional cut away view of an elongated cylindricalalkaline cell having the cathode of the invention.

FIG. 2 is a cross sectional view of a cylindrical button alkaline cellhaving the cathode of the invention.

DETAILED DESCRIPTION

A representative alkaline cell utilizing the cathode mixture of theinvention is shown in FIG. 1. The alkaline cell 810 comprises acylindrical casing 820 of steel, preferably nickel plated steel, havinga closed end 814 and an open end 816. The cell is preferably filled withan anode mixture 815 comprising zinc anode active material and a cathodemixture 812 of the invention comprising copper oxide (CuO) or copperhydroxide cathode active material. (The terms anode active material andcathode active material as used herein means the chemical material inthe anode and cathode, respectively, which undergoes electrochemicalreaction during cell discharge.) The cathode active material desirablycomprises between about 80 and 92 percent by weight of the cathodemixture 812.

The cathode mixture 812 comprises a graphitic carbon material, desirablyexpanded graphite particles or graphitic carbon nanofiber and anymixture thereof. In such case the total conductive carbon in the cathodemixture desirably comprises between about 3 and 10 percent by weight ofthe cathode, preferably between about 4 and 10 percent by weight of thecathode. The graphitic carbon additive can be comprised essentially ofexpanded graphite or graphitic carbon nanofibers. Preferably, thecathode mixture comprises between about 3 and 10 percent by weight,preferably between 4 and 10 percent by weight of the graphitic carbonnanofibers. Desirably, the conductive material can be composedessentially entirely of graphitic carbon nanofiber.

The cathode mixture 812 also desirably comprises between about 5 and 10percent by weight of an aqueous solution of KOH, which preferably has astrength of between about 7 and 9 Normal (30 and 40 wt. % KOH). Theresistivity of pure copper oxide or copper hydroxide is high and thusunsuitable as a cathode active material without a highly conductiveadditive. The addition of graphitic carbon nanofibers or expandedgraphite in amount preferably between about 4 and 10 percent by weightto a cathode mixture comprising high percentage copper oxide or copperhydroxide, e.g. over 75 percent by weight, reduces the resistivity ofthe mixture quite dramatically. The addition of graphitic carbonnanofibers to the cathode mixture can reduce the cathode resistivityeven more than the same amount of expanded graphite additive. Theaddition of expanded graphite or graphitic carbon nanofibers to cathodescomprising copper oxide or copper hydroxide cathode active materialmakes it possible to use the cell as a replacement for conventionalZn/MnO2 alkaline cells for use in normal discharge regimes. Additionallyat low discharge rates, e.g. at a level of about 9 mAmp, the alkalinecell of the invention exhibits even higher capacity (mAmp-hrs) thanconventional Zn/MnO2 alkaline cells. Thus, the addition of the expandedgraphite or graphitic carbon nanofibers in small amount between about 3and 10 percent by weight, preferably between 4 and 10 percent by weight,changes a cathode active material such as copper oxide or copperhydroxide from a material that is essentially not useful as a cathodematerial for alkaline cells to a material which exhibits very gooddischarge performance characteristics in such cell.

Similarly it has been determined that such graphitic carbon nanofiberscan be beneficially added to zinc alkaline cells having a cathode activematerial comprising copper oxide (CuO) or copper hydroxide (Cu(OH)₂).The addition of such graphitic carbon nanofibers, e.g. in amount betweenabout 3 and 10 percent by weight, desirably between about 4 and 10percent by weight, typically between 4 and 8 percent by weight of analkaline cell cathode comprising copper oxide or copper hydroxide,reduces the cathode resistivity quite substantially. This raises therunning voltage of the cell and increases the cell capacity (mAmp-hrs).

The term “graphite” or “graphitic material” as used herein shall includenatural and synthetic crystalline graphites, expanded graphites,graphitic carbons, and graphitic carbon fibers. A graphitic carbon hasthe characteristics of an ordered three-dimensional graphite crystallinestructure consisting of layers of hexagonally arranged carbon atomsstacked parallel to each other as determined by X-ray diffraction. Asdefined in International Committee for Characterization and Terminologyof Carbon (ICCTC, 1982), published in the Journal Carbon, Vol. 20, p.445 a graphitic carbon embraces the varieties of substances consistingof elemental carbon in allotropic form of graphite irrespective of ofstructural defects. The term graphitic carbon as used herein shall beconstrued in this manner.

The term carbon fibers shall mean elongated strands of carbon havinglength to diameter ratio greater than 4, typically greater than 8. Thelength to diameter ratio of carbon fibers can be much higher, forexample, greater than 100 or more. The term “natural crystallinegraphite” as used herein shall mean graphite that is minimallyprocessed, i.e., essentially in its geologically occurring naturalcrystalline form. The term “synthetic graphite” as used herein shallmean synthetically prepared or processed graphite. The term “syntheticgraphite” as used herein unless further qualified is also intended toinclude expanded forms of graphite (including expanded graphite that hasbeen exfoliated) and graphitic carbon nanofibers. The term “expandedgraphite” is a recognized term of art, for example, the form of graphitegenerally as referenced in U.S. Pat. No. 5,482,798. The expandedgraphite is preferably in particulate form having a mean averageparticle size desirably between about 0.5 micron and 50 micron,typically between about 10 micron and 50 micron. Further, expandedgraphite as used herein can be formed from natural and/or syntheticnon-expanded graphite particles processed so as to have a uniaxiallyexpanded crystal lattice. The extent of uniaxial expansion can besufficiently large such that the expanded graphite particles cancompletely exfoliate (i.e., separate into thin laminae). The term“flaky” as commonly used in connection with graphites, (i.e., natural orsynthetic flaky graphites) is intended to reflect that such graphiteshave a plate-like, non-expanded particle form.

It has been determined that use of graphitic carbon nanofibers in thecathode mixture of the invention employing copper oxide or copperhydroxide, is particularly useful. The addition of the graphitic carbonnanofibers has a very significant effect in raising the running voltageof the cell and significantly increases the useful life of the cell. Thegraphitic carbon nanofibers can desirably be added in amount betweenabout 3 and 10 percent by weight, preferably 4 to 10 percent by weightof the cathode mixture. Such carbon nanofibers can serve as the onlygraphite conductive material for the cathode or it can be admixed in theabove amount or smaller amount with other graphite materials such asnatural graphites and. Such graphitic carbon nanofibers, per se, arereferenced in the published art and specific methods of manufacture aredisclosed, for example, in U.S. Pat. Nos. 5,594,060; 5,846,509 and6,156,256.

The term graphitic carbon fibers as used herein shall mean carbon fibershaving a graphitic carbon structure as defined by the InternationalCommittee for Characterization and Terminology of Carbon (ICCTC, 1982),published in the Journal Carbon, Vol. 20, p. 445. The graphitic carbonnanofibers as used herein shall mean graphitic carbon fibers having amean average diameter less than 1000 nanometers (less than 1000×10⁻⁹meters). Preferably, the graphitic carbon nanofibers have a mean averagediameter less than 500 nanometer, more preferably less than 300nanometers. Desirably the graphitic carbon nanofibers have a meanaverage diameter between about 50 and 300 nanometers, typically betweenabout 50 and 250 nanometers. The graphitic carbon nanofiber useful inthe cathode mixture 812 of the invention has a mean average diameterdesirably less than about 300 nanometers, preferably between about 50and 250 nanometers, typically about 200 nanometers. The mean averagelength of the carbon nanofibers is desirably between about 0.5 and 300micron, typically about 200 micron. The graphitic carbon nanofibers canhave a BET surface area between about 15 and 50 m²/g, typically between15 and 30 m²/g.

A preferred graphitic carbon nanofiber for use in the cathode mixture812 of the invention is a vapor grown graphitic carbon fiber availableunder the trade designation PR19HT carbon fibers from Applied Sciences,Cedarville, Ohio. Such graphitic carbon nanofibers can be made byhydrocarbon vapor pyrolysis methods described, for example, in AppliedSciences U.S. Pat. No. 6,156,256; U.S. Pat. No. 5,846,509; and U.S. Pat.No. 5,594,060 herein incorporated by reference. The resulting carbonnanofibers have a graphitic carbon structure as defined in InternationalCommittee for Characterization and Terminology of Carbon (ICCTC, 1982),published in the Journal Carbon, Vol. 20, p. 445. The vapor grown carbonfibers described in the above patent references are graphitic carbonfibers which can be made by the pyrolysis of hydrocarbon, for example,methane in a gas phase reaction at temperatures of around 1000° C. orhigher. The gas phase reaction involving the hydrocarbon is carried outupon contact with metal particles, typically iron particles in anonoxidizing gas stream. The iron particles catalyze the growth of verythin individual carbon fibers (e.g. carbon nanofibers) which have agraphitic carbon structure. The resulting carbon fibers can have a verythin diameter (nanofibers), for example, between 50 and 300 nanometerssuch as that available under the trade designation PR19HT graphiticcarbon nanofibers (Applied Sciences).

A specific method of forming such graphitic carbon nanofibers isdescribed, for example, in U.S. Pat. No. 6,156,256 as follows: Theprocess includes the steps of providing in a reactor a first catalystpreferably in the form of solid particles having a size from 10nanometers to 1000 nanometers, which is used to initiate the formationof the nanofibers. The first catalyst in the form of solid particles canbe an iron catalyst, desirably iron sulfide. Other materials which canbe used as solid particles for the first catalyst are listed in U.S.Pat. No. 6,156,256 as iron, nickel, cobalt, ferrocene, alloys of iron,alloys of nickel, alloys of cobalt, sulfur, iron sulfide, and nickelnitrate. A vacuum is applied to the reactor to create reduced pressurein the reactor. A carbon-based gas is introduced into the reactor. Thecarbon-based gas is a gas which forms carbon and hydrogen free-radicalspecies upon pyrolysis. The carbon based gas as stated in U.S. Pat. No.6,156,256 is desirably methane. However, as stated in this reference itcan also be carbon dioxide, methane, ethane, propane, ethene, naturalgas, and coal derivative gases and mixtures thereof. The reaction gasmixture desirably also comprises hydrogen. The hydrogen is provided toinhibit pyrolytic fattening of the nanofibers and to inhibit theformation of soot during the pyrolysis reaction. As indicated in U.S.Pat. No. 6,156,256 the reaction gas mixture used to form the nanofibersdesirably comprises from 40 to 90 percent of hydrogen gas and from 10 to60% of the carbon based gas, desirably a 50—50 mixture of the carbonbased gas and hydrogen. As described in U.S. Pat. No. 6,156,256 a secondgrowth catalyst may be used in admixture with the carbon-based gas andhydrogen gas. The second catalyst promotes diametric growth (growth ofdiameter) of the nanofibers. As stated in this reference the secondcatalyst is desirably ammonia. However, it may include hydrogen andammonia and mixtures thereof.

To form the nanofibers the above gases are introduced into the reactor.Formation of the fibers can be carried out at reduced pressure of fromabout 10 to 100 Torr, desirably from about 20 to 50 Torr. The mixture ofgases can be formed into a plasma by means of a plasma generating sourcepreferably a microwave generator, but may also be a hot filament, radiofrequency (RF) generator, or by an electrical discharge generator. Whenthe first catalyst is formed of the above described solid particles theyare desirably supported on a substrate such as an inert dielectricmaterial such as quartz, ceramic and refractory materials, preferablyceramic material which can be placed within the reactor, desirablywithin the reactor feed inlet. The reactor itself is constructed ofmaterials which are resistient to heat and corrosion, for examplenickel, high temperatre steel, quartz, ceramic, and refractory material.Power is turned on and the reactor heated. The mixture of gases is thenformed into a plasma within the reactor at above described reducedpressure and at a catalyst substrate temperature of about 800° C. to1200° C., desirably a temperature between about 800° C. and 1000° C. Thegas rate can typically be between 20 and 1000 scfm (standard cubic feetper minute), desirably about 100 scfm. If a microwave power source isused, the latter reference describes generating between about 600 and1200 Watts of power to convert the carbon-based gas to gas plasmacatalyzed by the above mentioned solid catalyst. The plasma gas containscarbon free-radicals, hydrogen free radicals, and oxygen free-radicals.The carbon is captured by the catalyst to form the graphitic carbonnanofibers. The power supply is discontinued once the desired amount ofnanofibers are formed. In another approach as described in U.S. Pat. No.6,156,256 the first catalyst can be in a gaseous state instead of beingprovided in the form of solid particles. Suitable gaseous catalysts aredescribed as being selected from iron pentacarbonyl, hydrogen sulfide,and a ferrocene-xylene mixture. If such gaseous catalyst is employed, itmay be supplied in combination with the carbon-based gas and hydrogenmixture. In this embodiment the graphitic carbon nanofibers can beproduced in steady state and collected as they are formed.

The graphitic carbon nanofibers contain impurities which are residualamount of the catalyst, typically iron or iron compound (or other metalor material above described), which were used to catalyze the gas phasereaction. It has been determined by Applicants herein that if suchimpurities are removed, a highly desirable conductive carbon nanofiberis obtained. Such purified graphitic carbon nanofiber can be addedadvantageously in nominal amount (e.g. 3 to 10 percent by weight) tocathode active material such as copper oxide or copper hydroxide. Theaddition of the purified graphitic carbon nanofibers to alkaline cellcathode mixtures comprising copper oxide or copper hydroxide, improvesthe cathode electrical conductivity very significantly. It is not knownwith certainty why this occurs. The very thin graphitic carbonnanofibers fibers appear to increase the number of electrical contactpoints and conductive pathways between the individual copper oxide orcopper hydroxide particles more than the same percent by weight ofconventional graphites. The tendency of the graphitic carbon nanofiberto attach to the copper oxide or copper hydroxide particles may beanother favorable factor. This in turn causes the cathode to become moreconductive and improves cell performance.

It has been determined that the iron (or other metal) impurity which areresidual catalyst impurities imbedded in the graphitic carbon nanofibercan be readily removed therefrom by subjecting the nanofibers to heatingat temperatures between about 2500° C. and 3100° C. after the fibershave been formed. Such heating vaporizes the metal impurities and canalso serve to further graphitize the carbon fiber, particularly thesurface of the fibers. The end result is a purified graphitic carbonnanofiber desirably contains less than 200 ppm, preferably less than 100ppm, more preferably less than 50 ppm metal. (The term “metal” shallinclude all metal whether in elemental, ionic or chemically bound incompounds. PPM is parts by weight metal per million parts by weightcarbon in the carbon fibers.) In particular the iron content in thegraphitic carbon nanofibers is below the above stated cutoff amounts inppm. Such graphitic carbon nanofiber when added in amount, for example,between about 3 and 10 percent by weight, preferably between about 4 and10 percent by weight of cathodes comprising highly resistant copperoxide or copper hydroxide cathode active material, can verysignificantly lower the resistivity of the cathode. This in turn canmake such cathodes very suitable for use in alkaline cells, particularlyalkaline cells having an anode comprising zinc and electrolytecomprising aqueous potassium hydroxide.

The cathode mixture 812 includes an aqueous KOH electrolyte solution andthe mixture can be prepared wet, with aqueous KOH included before themixture is inserted into the cell. For example, the casing 820 can befilled with the cathode mixture and the central portion of the cathodemixture can be excavated leaving the annular cathode 812 as shown inFIG. 1. The wet cathode mixture can be compacted while in the cell.Alternatively, the wet mixture can be compacted into disks 812 a beforeinsertion into the cell and then, optionally, additionally compactedwhile in the cell. Alternatively, the cathode mixture 812 can beprepared by first dry mixing the copper oxide or copper hydroxide, andgraphitic carbon material. The dry mixture can be compacted into thecell casing 820 or can be compacted into disk shaped blocks 812 a, whichcan be inserted into the cell in stacked arrangement. A separator sheet890 can be placed against the inside surface of cathode disks 812 a.Generally, separators conventionally used in zinc/MnO₂ alkaline cellscan be used for separator 890 in the present cell 810 having a cathode612 comprising copper oxide or copper hydroxide. Separator 890 can be ofcellulosic film or a film formed of nonwoven material comprisingpolyvinylalcohol and rayon fibers. Separator 890 can be of a singlelayer of such nonwoven material or can be a composite having an outerlayer of cellophane adhered to the nonwoven material. The nonwovenmaterial can typically contain between about 60 weight percent to 80weight percent poyvinylalcohol fibers and between about 20 and 40 weightpercent rayon fibers. Separator 890 can be positioned so that thecellophane layer is adjacent either cathode 812 or anode 815. The abovedescribed separators are known and have been used in connection withconventional zinc/MnO₂ alkaline cell and are also suitable for use inthe present alkaline cell 810. Aqueous KOH electrolyte can be pouredover the dry cathode wherein it becomes absorbed into the separator andcathode. The anode material 815 can then be added to the cell.

The copper oxide for use in cathode 812 is a powder having an averageparticle size (dry) desirably between about 1 and 100 micron, typicallyabout 10 micron. The copper oxide has a purity greater than 99 percentby weight, preferably between about 99 and 99.8 percent by weight. Thecopper oxide has a real density of about 6.4 g/. The real density of asolid is the weight of the sample divided by the real volume. The realvolume of a sample is the actual volume less volume occupied byentrapped air between the particles and pores within the particles. TheBET surface area (m²/g) (Brunauer, Emmett and Taylor method) is thestandard measurement of particulate surface area by gas (nitrogen and/orother gasses) porosimetry as is recognized in the art. The BET surfacearea measures the total surface area on the exterior surface of theparticle and also that portion of surface area defined by the open poreswithin the particle available for gas adsorption and deadsorption whenapplied. BET surface area determinations as reported herein is carriedout in accordance with ASTM Standard Test Method D4820-99.

Anode 815 comprises zinc and aqueous KOH electrolyte. The electrolyte inthe anode comprises a conventional mixture of KOH, ZnO and gellingagent. The zinc serves as the anode active material. The anode andcathode can be separated by a conventional ion porous separator 890, forexample, comprising polyvinylalcohol and cellulosic fibrous material.After cell 810 is filled an insulating plug 860 is inserted into openend 816. Insulating plug 860 may be of polypropylene, talc filledpolypropylene, sulfonated polyethylene or nylon. Plug 860 can have athinned portion 865 therein typically of a small circular, oval orpolygonal shape. Thinned portion 865 functions as a rupturable membranewhich can be designed to rupture thereby releasing excessive gas withinthe cell. This guards against excessive buildup of gas pressure withinthe cell, for example, if the cell is subjected to excessive heat orabusive operating conditions. The plug 860 is preferably snap fittedaround circumferential step 818 as shown in the figure so that the pluglocks in place into the open end 816. The peripheral edge 827 of casing820 is crimped over the top of insulating plug 860. A paper insulatingwasher 880 is applied over the crimped peripheral edge 827 of casing820. Insulating washer 880 can be a polyethylene coated paper washer. Aterminal end cap 830 is welded to the head of current collector 840. Anelongated current collector 840 is then inserted (force fitted) intoaperture 844 of insulating plug 860 so that end cap 830 comes to restagainst insulating washer 880. Current collector 840 can be selectedfrom a variety of known electrically conductive metals found to beuseful as current collector materials, for example, brass, tin platedbrass, bronze, copper or indium plated brass. The current collector 840used in the test cells was of brass. Conventional asphalt sealant may bepreapplied around the current collector 840 before it is inserted intoaperture 844. A film label 870 is applied around casing 820. Theterminal end cap 830 becomes the negative terminal of alkaline cell 810and pip 825 at the closed end of casing 820 becomes the positiveterminal.

The cell 810 shown in FIG. 1 can be an AA cell. However, the alkalinecell shown in the figure is not intended to be restricted to anyparticular size. Thus, the present invention is applicable to AAAA, AAA,C and D size cylindrical alkaline cells as well as button size alkalinecells of any size or shape. Alkaline cell 810 is not intended to berestricted to any particular alkaline cell chemistry or cell size,except that the cathode 812 is prepared utilizing the cathode mixturesof invention employing copper oxide or copper hydroxide cathode activematerial and a graphitic carbon additive, preferably expanded graphiteor graphitic carbon nanofibers or any mixture thereof. The above cell(FIG. 1) can be an AAAA, AAA, AA, C or D cells. These standard cellsizes are recognized in the art and are set by the American Nationalstandards Association or in Europe by the International ElectrotechnicalCommission (IEC). The AA cylindrical cell as referenced herein hadstandard overall dimensions as given by the American National StandardsInstitute (ANSI) battery specification ANSI C18.1M, Part 1-1999 asfollows: The overall length from positive and negative terminal tips isbetween 49.2 mm and 50.5 mm and overall outside cell diameter is between13.5 mm and 14.5 mm.

Thus cell 810 can contain conventional alkaline cell anode chemistriesincluding those which contain zero added mercury (less than 50 partsmercury per million parts total cell weight, preferably less than 10parts mercury per million parts total cell weight) and modificationsthereof. Such representative chemistries, for example, are disclosed inU.S. Patent No. 5,401,590, herein incorporated by reference. The cell810 of the invention also preferably does not contain added amounts oflead and thus can be essentially lead free, that is, the total leadcontent is less than 30 ppm, desirably less than 15 ppm of total metalcontent of the anode.

A zinc/manganese dioxide alkaline cell also can be fabricated in theform of a button or coin cell 110 as shown in FIG. 2. The cell 110 caninclude a cathode 170 comprising the cathode mixture of the invention.Such cathode mixtures, for example, can comprise copper oxide, 80 to 92wt. %, graphitic carbon, preferably expanded or graphitic carbonnanofibers between about 4 and 10 wt. %, and between about 5 and 10 wt.% of aqueous KOH electrolyte (aqueous KOH electrolyte is 30 to 40 wt. %KOH concentration, preferably between 35 and 40 wt. % KOHconcentration). The aqueous KOH electrolyte preferably also containsabout 2 wt. % ZnO. The cathode mixture can optionally also comprisebetween about 0.1 to 0.5 wt % of a polyethylene binder. The addition ofexpanded graphitic carbon nanofibers in amount between about 3 and 10percent by weight, preferably between about 4 and 8 percent by weight ofthe allows cathodes having a high loading of copper oxide, e.g. betweenabout 80 and 92 percent by weight copper oxide, to be used successfullyin alkaline cells.

The anode material 150 comprises: Zinc alloy powder 62 to 69 wt % (99.9wt % zinc containing indium), an aqueous KOH solution comprising 38 wt %KOH and about 2 wt % ZnO; a cross-linked acrylic acid polymer gellingagent available commercially under the tradename “CARBOPOL C940” from B.F. Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrilegrafted onto a starch backbone commercially available commercially underthe tradename “Waterlock A-221” from Grain Processing Co. (between 0.01and 0.5 wt. %); dionyl phenol phosphate ester surfactant availablecommercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm).The zinc alloy average particle size is desirably between about 30 and350 micron. The bulk density of the zinc in the anode (anode porosity)is between about 1.75 and 2.2 grams zinc per cubic centimeter of anode.The percent by volume of the aqueous electrolyte solution in the anodeis between about 69.2 and 75.5 percent by volume of the anode. It shallbe understood that the term zinc as used herein shall include such zincalloy powder, since the alloy powder is composed almost entirely of zincand functions electrochemically as zinc.

The separator 160 can be a conventional ion porous separator asdescribed above with respect to separator 890. In the specificembodiment shown in FIG. 2, referenced in the examples, the separator160 comprises an outer layer of cellulose and an inner layer of anonwoven material composed of cellulosic (rayon) and polyvinylalcoholfibers. Separator 160 is positioned so the outer layer of celluloseabuts the cathode 170. In the button cell 110 shown in FIG. 2, adisk-shaped cylindrical housing 130 is formed having an open end 132 anda closed end 138. Housing 130 is formed from nickel-plated steel. Anelectrical insulating member 140, preferably a cylindrical member havinga hollow core, is inserted into housing 130 so that the outside surfaceof insulating member 140 abuts and lines the inside surface of housing130. Alternatively, the inside surface of housing 130 can be coated witha polymeric material that solidifies into insulator 140 abutting theinside surface housing 130. Insulator 140 can be formed from a varietyof thermally stable insulating materials, for example, nylon orpolypropylene.

The cathode mixture 170 comprising copper oxide or copper hydroxide,graphitic carbon, preferably comprising expanded graphite or graphiticcarbon nanofibers, and mixtures thereof, and aqueous electrolyte can beprepared by simple mixing at ambient temperature in a conventionalblender until a homogenous mixture is obtained. The cathode 170 isapplied as a layer or a pressed disk abutting the inside surface of theclosed end 138 of housing 130. The separator sheet 160 is placedoverlying cathode 170. Additional aqueous electrolyte can be added sothat electrolyte fully penetrates through separator sheet 160 andcathode 170. A layer of anode mixture 150 comprising particulate zinc,aqueous KOH electrolyte solution (35-40 wt % KOH and 2 wt. % ZnO), andgelling agent is applied to the separator sheet 160. The anode cover120, formed preferably of nickel-plated steel, is inserted into the openend 132 of housing 130. An anode current collector 115 comprising asheet of brass, tin-plated brass, bronze, copper or indium-plated brasscan optionally be welded to the inside surface of anode cover 120.Peripheral edge 135 of housing 130 is crimped over the exposed insulatoredge 142 of insulating member 140. The peripheral edge 135 bites intoinsulator edge 142 closing housing 130 and tightly sealing the cellcontents therein. The anode cover 120 also functions as the negativeterminal of the cell and the housing 130 at the closed end 138 functionsas the cell's positive terminal.

Test cylindrical button cells 110 had a diameter of 15.0 mm and depth ofabout 8.2 mm.

The separator 160 was a conventional ion porous separator consisting ofan inner layer of a nonwoven material of cellulosic (rayon) andpolyvinylalcohol fibers and an outer layer of cellophane. The same anodemixture comprising particulate zinc was used in each test cell. Thecathode composition was varied as indicated in following examples. Theperformance of the cells, service life (milliamp-hrs) and energy output(milliwatt-hrs) at low rate was determined by discharging at 22 milliAmpto a cut off voltage of 0.1 Volts.

In the case of the comparative test (Examples 1A-1C) using an anodecomprising zinc and a cathode comprising MnO₂, the cells 110 and 810were balanced on the basis that milliamp-hrs capacity of zinc (based on820 milliamp-hours per gram zinc) divided by the milliamp-hrs capacityof MnO₂ (based on 308 milliamp-hours per gram MnO₂) is above about 1.0.This assures that cell discharge is limited by the cathode. In the cellstested (Examples 2A-2C) using an anode comprising zinc and cathodecomprising copper oxide the cells 110 and 810 were balanced on the basisthat the milliamp-hrs capacity of zinc (based on 820 milliamp-hours pergram zinc) divided by the milliamp-hrs capacity of copper oxide (basedon 674 milliAmp-hours per gram copper oxide) is above about 1.0. In thecells tested (Examples 3A-3C) using an anode comprising zinc and cathodecomprising copper hydroxide the cells 110 and 820 were balanced on thebasis that the milliAmp-hrs capacity of zinc (based on 820milliAmp-hours per gram zinc) divided by the milliAmp-hrs capacity ofcopper hydroxide (based on 549 milliAmp-hours per gram copper hydroxide)is above about 1.0.

EXAMPLE 1A Comparative—Zinc Anode; MnO2 Cathode with Natural Graphite

Test cylindrical cells 110 were prepared. The cell 10 had an overalldimension of about 15 mm diameter and depth of about 8.2 mm. The totalinternal volume of cell 110 available for cathode 170 and anode 150 wasabout 1.2 cubic centimeters. Test cells 110 were prepared with a anode150 comprising Zinc alloy powder 62 to 69 wt % (99.9 wt % zinccontaining indium), an aqueous KOH solution comprising 38 wt % KOH andabout 2 wt % ZnO; a cross-linked acrylic acid polymer gelling agentavailable commercially under the trade name “CARBOPOL C940” from B. F.Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrilegrafted onto a starch backbone commercially available commercially underthe tradename “Waterlock A-221” from Grain Processing Co. (between 0.01and 0.5 wt. %); dionyl phenol phosphate ester surfactant availablecommercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm).The zinc alloy average particle size is desirably between about 30 and350 micron. The bulk density of the zinc in the anode is between about1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent byvolume of the aqueous electrolyte solution in the anode is between about69.2 and 75.5 percent by volume of the anode.

The cathode 170 can have the following representative composition: 80-87wt % of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee),4-10 wt % graphite (e.g. natural graphite NdG-15 from Nacional deGraphite, Brazil, BET surface of 8.1 m²/g), 5-10 wt % of an aqueous KOHsolution having a KOH concentration of about 35-40 wt. %, and optionally0.1-0.5 wt. % of a polyethylene binder such as Coathylene binder fromHoechst Celanese. The cathode 170 had 0.54 grams of MnO₂ and wasbalanced as above described. The amount of zinc in anode 150 was in someexcess to make the cell discharge cathode limited. A specific cathodecomposition which was used for Example 1A is as follows:

Cathode Composition¹ Wt. % Vol. % MnO₂ (EMD) 87.6 72.20 (Trona D)Natural graphite² 5.5 9.00 (NdG-15) KOH aqueous 6.5 17.50 Solution (38wt % KOH and 2 wt % ZnO) Polyethylene 0.4 1.30 Binder 100.0 100.00Notes: ¹The wt. % values have been converted from vol. % using thefollowing real densities: MnO₂ (EMD), 4.45 g/cc; natural graphite (2.25g/cc); and 38 wt % KOH aqueous solution (1.37 g/cc). ²Natural graphiteNdg-15 from Nacional de Graphite, Brazil.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. The 22 milliAmp discharge for this cell isequivalent to a current density of about 21 milliAmp/cm² based on theanode/cathode interface, approximately equivalent to a 250 milliAmpconstant discharge rate for a AA size cell as in FIG. 2. The cell had atime averaged running voltage of about 0.91 volts. The capacity obtainedat the above cut off voltage was 161 milliAmp-hrs. Specific capacity ofthe MnO₂ is 782 milliAmp-hrs per cubic centimeter of total cathodevolume (292 milliAmp-hrs per gram MnO₂). The energy output of the cellwas 147 milliWatt-hrs. The energy output of the cathode is 715milliWatt-hrs per cubic centimeter. The cathode 170 had a resistivity of0.335 ohm-meters.

EXAMPLE 1B Comparative Zn Anode; MnO2 Cathode with Expanded Graphite

The same cell as in Example 1A was prepared except that the naturalgraphite in the cathode was replaced with expanded graphite. The cathodecomposition was as follows:

Cathode Composition¹ Wt. % Vol. % MnO₂ (EMD) 87.6 72.2 (Trona D)Expanded graphite² 5.5 9.0 (WH20) KOH aqueous 6.5 17.5 Solution (38 wt %KOH and 2 wt % ZnO) Polyethylene 0.4 1.3 Binder 100.0 100.00 Notes: ¹Thewt. % values have been converted from vol. % using the following realdensities: MnO₂ (EMD), 4.45 g/cc; natural graphite (2.25 g/cc); and 38wt % KOH aqueous solution (1.37 g/cc). ²Expanded graphite WH20 fromChuetsu Company.

The cell 110 is discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equivalent to a constant current discharge of about 250milliAmp in a AA size cell as in FIG. 2. The cell had a time averagedrunning voltage of about 1.01 volts. The capacity obtained at the abovecut off voltage was 156 milliAmp-hrs. The specific capacity of the MnO₂was 792 milliAmp-hours per cubic centimeter of total cathode volume(289milliAmp-hrs per gram MnO₂). The energy output of the cell was 158milliWatt-hrs. The resistivity of cathode 170 was 0.075 ohm-meter.

EXAMPLE 1C Comparative Zn Anode; MnO2 Cathode with Graphitic CarbonNanofibers

The same cell as in Example 1A was prepared except that the naturalgraphite in the cathode was replaced with graphitic carbon nanofibers.The cathode composition was as follows:

Cathode Composition¹ Wt. % Vol. % MnO₂ (EMD) 87.6 72.20 (Trona D) carbonnanofibers² 5.5 9.00 (NdG-15) KOH aqueous 6.5 17.50 Solution (38 wt %KOH and 2 wt % ZnO) Polyethylene 0.4 1.30 Binder 100.0 100.00 Notes:¹The wt. % values have been converted from vol. % using the followingreal densities: MnO₂ (EMD), 4.45 g/cc; natural graphite (2.25 g/cc); and38 wt % KOH aqueous solution (1.37 g/cc). ²Graphitic carbon nanofiberfrom Applied Sciences, Cedarville, Ohio., post heat treated attemperatures of between about 2500° C. and 3100° C. The fibers had anaverage diameter of 200 nanometer and average length of 200 micron.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This rate is equivalent to a current densityof about 21 milliAmp/cm² based on the anode/cathode interface,approximately equivalent to a discharge rate of 250 milliAmp for an AAsize cell as in FIG. 2. The cell had a time averaged running voltage ofabout 1.01 volts. The capacity obtained at the above cut off voltage was155 milliAmp-hrs. Specific capacity of the MnO₂ was 814 milliAmp-hrs percubic centimeter of cathode (286 milliAmp-hrs per gram MnO₂). The energyoutput of the cell was 157 milliWatt-hrs. The resistivity of cathode 170was 0.022 ohm-meters.

The cell performance of Examples 1A-1C is summarized in Table 1.

EXAMPLE 2A Zn Anode; Copper Oxide Cathode with Natural Graphite

Test cell 110 was prepared as in Example 1A except that the cathode 170is formed of the following cathode mixture of the invention comprisingcopper oxide (CuO). The CuO was ACS (American Chemical Society) grade at99.5 wt. % purity obtained from Fisher Scientific Company. Graphiticmaterial in the form of natural graphite, NdG-15 from Nacional DeGraphite, Brazil was added as in Example 1A. The cathode 170 had 0.78grams of copper oxide and was balanced with zinc in excess in anode 150as above described. Cathode 170 had the following composition.

Cathode Composition¹ Wt. % Vol. % CuO 91.0 72.2 Natural graphite² 4.09.0 (NdG-15) KOH aqueous 4.7 17.5 Solution (38 wt % KOH and 2 wt. % ZnO)Polyethylene 0.3 1.3 Binder 100.00 100.00 Notes: ¹The wt. % values havebeen converted from vol. % using the following real densities: CuO, 6.4g/cc; natural graphite, (2.25 g/cc); and 38 wt % KOH aqueous solution(1.37 g/cc). ²Natural graphite Ndg-15 from Nacional de Graphite, Brazil.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. The 22 milliAmp discharge for this cell(current density of about 21 milliAmp/cm²) is approximately equivalentto a 250 milliAmp discharge rate for a AA size cell as in FIG. 2. Thecell had a time averaged running voltage of about 0.74 volts. Thecapacity obtained at the above cut off voltage was 506 milliAmp-hrs. Thespecific capacity of the copper oxide was was 253 milliAmp-hours percubic centimeter total cathode volume(661 milliAmp-hrs per gram copperoxide). The energy output of the cell was 373 milliWatt-hrs. The cathodehad a resistivity of 0.344 ohm-meter.

EXAMPLE 2B Zn Anode; Copper Oxide Cathode with Expanded Graphite

Test cell 110 is prepared as in Example 1B except that the cathode 170is formed of the following cathode mixture of the invention comprisingcopper oxide (CuO). The CuO was ACS (American Chemical Society) grade at99.5 wt. % purity obtained from Fisher Scientific Company. Graphitematerial in the form of expanded graphite, WH20 from Chuetsu Company wasadded as in Example 1B. The cathode 170 had 0.78 grams of copper oxideand was balanced with zinc in excess in anode 150 as above described.

Cathode Composition¹ Wt. % Vol. % CuO 91.0 72.2 Expanded graphite² 4.09.0 (WH20) KOH aqueous 4.7 17.5 Solution (38 wt % KOH and 2 wt. % ZnO)Polyethylene 0.3 1.3 Binder 100.00 100.00 Notes: ¹The wt. % values havebeen converted from vol. % using the following real densities: CuO, 6.4g/cc; expanded graphite, (2.25 g/cc); and 38 wt % KOH aqueous solution(1.37 g/cc). ²Expanded graphite WH20 from Chuetsu Company.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm², approximately equal to constant current dischargeof about 250 milliAmp in a AA size cell as in FIG. 2. The cell had atime averaged running voltage of about 0.74 volts. The capacity obtainedat the above cut off voltage was 518 milliAmp-hrs. The specific capacityof the copper oxide was 2363 milliAmp per cubic centimeter total cathodevolume (657 milliAmp per gram copper oxide). The energy output of thecell was 383 milliWatt-hrs. The resistivity of cathode 170 was 0.054ohm-meters.

EXAMPLE 2C Zn Anode; Copper Oxide Cathode with Graphitic CarbonNanofibers

Test cell 110 was prepared as in Example 1C except that the cathode 170was formed of the following cathode mixture of the invention comprisingcopper oxide (CuO). The CuO was ACS (American Chemical Society) grade at99.5 wt. % purity obtained from Fisher Scientific Company. Graphiticmaterial in the form of graphitic carbon nanofibers PR19HT (200nanometer diameter and 200 micron length) from Applied Sciences wasadded as in Example 1C. The cathode 170 has 0.78 grams copper oxide andis balanced with an amount of zinc in anode 150 in excess as abovedescribed.

Cathode Composition¹ Wt. % Vol. % CuO 91.0 72.2 Carbon nanofibers² 4.09.0 (PR19HT) KOH aqueous 4.7 17.5 Solution (38 wt % KOH and 2 wt. % ZnO)Polyethylene 0.3 1.3 Binder 100.00 100.00 Notes: ¹The wt. % values havebeen converted from vol. % using the following real densities: CuO 6.4g/cc; graphitic carbon nanofibers PR19HT from Applied Sciences, (2.25g/cc); and KOH aqueous solution (1.37 g/cc), polyethylene binder is 1.0g/cc. ²Graphitic carbon nanofiber from Applied Sciences, Cedarville,Ohio, post heat treated at temperature between about 2500° C. and 3100°C. The fibers had an average diameter of 200 nanometer and averagelength of 200 micron.

The cell 110 is discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equal to a current drain of about 250 milliAmp for a AAsize cell as in FIG. 2. The cell had a time averaged running voltage ofabout 0.75 volts. The capacity obtained at the above cut off voltage was514 milliAmp-hrs. The specific capacity of the copper oxide was 257milliAmp-hours per cubic centimeter total cathode volume (639milliAmp-hours per gram copper oxide.) The energy output of the cell was387 milliWatt-hours. The cathode 170 had a resistivity of 0.054ohm-meters.

The cell performance of Examples 2A-2C is summarized in Table 2.

EXAMPLE 3A Zn Anode: Copper Hydroxide Cathode with Natural Graphite

Test cell 110 was prepared as in Example 1A except that the cathode 170is formed of the following cathode mixture embodiment comprisingresistive copper hydroxide Cu(OH)₂. Graphite material in the form ofnatural graphite was added as in Example 1A. The cathode 170 had 0.42grams of copper hydroxide and was balanced with zinc in excess in anode150 as above described.

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 Natural Graphite²7.0 9.0 (NdG-15) KOH aqueous 8.3 17.5 Solution (38 wt % KOH and 2 wt. %ZnO) Polyethylene 0.5 1.30 Binder 100.0 100.0 Notes: ¹The wt. % valueshave been converted from vol. % using the following real densities:Cu(OH)₂, 3.37 g/cc; natural graphite (2.25 g/cc); and 38 wt % KOHaqueous solution (1.37 g/cc); polyethylene binder, 1.0. The Cu(OH)₂ wasresistive copper hydroxide from Aldrich Chemical Co., Inc. Catalog#28,978.7 (assay less than 92 wt. % copper hydroxide). ²Natural graphiteNdg-15 from Nacional de Graphite, Brazil.

The cell 110 is discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm², approximately equivalent to a current drain ofabout 250 milliAmp in a AA size cell as in FIG. 2. The cell had a timeaveraged running voltage of about 0.64 volts. The capacity obtained atthis cut off voltage was 212 milliAmp-hrs. The specific capacity of thecopper hydroxide was 1,036 milliAmp per cubic centimeter total cathodevolume (506 milliAmp-hours per gram copper hydroxide). The energy outputof the cell was 136 milliWatt-hrs. The cathode 170 had a resistivity of234 ohm-meters.

EXAMPLE 3B Zn Anode: Copper Hydroxide Cathode with Expanded Graphite

Test cell 110 is prepared as in Example 1B except that the cathode 170was formed of the following cathode mixture embodiment comprisingresistive copper hydroxide Cu(OH)₂. Graphite material in the form ofexpanded graphite was added as in Example 1B. The cathode 170 had 0.42grams of copper hydroxide and was balanced with zinc in anode 150 inexcess as above described. The cathode 170 had the followingcomposition:

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 Expanded graphite²7.0 9.0 (WH20) KOH aqueous 8.3 17.5 Solution (38 wt % KOH and 2 wt. %ZnO) Polyethylene 0.5 1.30 Binder 100.0 100.0 Notes: ¹The wt. % valueshave been converted from vol. % using the following real densities:Cu(OH)₂, 3.37 g/cc; expanded graphite, (2.25 g/cc); and 38 wt % KOHaqueous solution (1.37 g/cc); polyethylene binder, 1.0. The Cu(OH)₂ wasresistive copper hydroxide from Aldrich Chemical Co., Inc. Catalog#28,978.7 (assay less than 92 wt. % copper hydroxide). ²Expandedgraphite WH20 from Chuetsu Company.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equal to a constant current discharge of about 250milliAmp in a AA size cell as in FIG. 2. The cell had a time averagedrunning voltage of about 0.62 volts. The capacity obtained at the abovecut off voltage was 204 milliAmp-hrs. The specific capacity of thecopper hydroxide was 978 milliAmp-hours per cubic centimeter totalcathode volume (480 milliAmp-hours per gram copper hydroxide). Theenergy output of the cell was 126 milliWatt-hrs. The cathode 170 had aresistivity of 2.6 ohm-meters.

EXAMPLE 3C Zn Anode; Copper Hydroxide Cathode with Graphitic CarbonNanofibers

Test cell 110 was prepared as in example 1C except that the cathode 170was formed of the following cathode mixture embodiment comprisingresistive copper hydroxide Cu(OH)₂. Graphite material in the form ofgraphitic carbon nanofibers was added as in Example 1C. The cathode 170had 0.42 grams of copper hydroxide and was balanced with zinc in anode150 as above described. Cathode 170 had the following composition:

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 carbon nanofiber²7.0 9.0 (PR19HT from Applied Sciences) KOH aqueous 8.3 17.5 Solution (38wt % KOH and 2 wt. % ZnO) Polyethylene 0.5 1.3 Binder 100.0 100.0 Notes:¹The wt. . % values have been converted from vol. % using the followingreal densities: Cu(OH)₂, 3.37 g/cc; graphitic carbon nanofiber, (2.25g/cc); and 38 wt % KOH aqueous solution (1.38 g/cc). The Cu(OH)₂ wasresistive copper hydroxide from Aldrich Chemical Co., Inc. Catalog#28,978.7 (assay less than 92 wt. % copper hydroxide). ²Graphitic carbonnanofiber from Applied Sciences, Cedarville, Ohio, post heat treated attemperatures between about 2500° C. and 3100° C. The fibers had anaverage diameter of 200 nanometer and average length of 200 micron.

The cell 110 is discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equal to a current drain of about 250 milliAmp in an AAsize cell as in FIG. 2. The cell had a time averaged running voltage ofabout 0.62 Volts. The capacity obtained at the above cut off voltage was209 milliAmp-hrs. The specific capacity of the copper hydroxide was 576milliAmp-hours per cubic centimeter total cathode volume (501milliAmp-hours per gram copper hydroxide). The energy output of the cellwas 130 milliWatt-hrs. The cathode 170 had a resistivity of 1.03ohm-meters.

The cell performance of Examples 3A-3C is summarized in Table 3.

EXAMPLE 4A Zn Anode: Copper Hydroxide Cathode with Natural Graphite

Test cell 110 was prepared as in example 3A except that the cathode 170is formed of the following cathode mixture embodiment comprising a lessresistive copper hydroxide Cu(OH)₂. Graphite material in the form ofnatural graphite was added as in example 3A. The cathode 170 had 0.42grams of copper hydroxide and was balanced with zinc in excess in anode150 as above described.

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 Natural Graphite²7.0 9.0 (NdG-15) KOH aqueous 8.3 17.5 Solution (38 wt % KOH and 2 wt. %ZnO) Polyethylene 0.5 1.30 Binder 100.0 100.0 Notes: ¹The wt. % valueshave been converted from vol. % using the following real densities:Cu(OH)₂, 3.37 g/cc; natural graphite, (2.25 g/cc); and 38 wt % KOHaqueous solution (1.37 g/cc); polyethylene binder, 1.0. . The Cu(OH)₂was lower resistive copper hydroxide from Alfa Aesar Company, stock#32733 (assay 94 wt % purity copper hydroxide). ²Natural graphite Ndg-15from Nacional de Graphite, Brazil.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equivalent to a current drain of about 250 milliAmp in aAA size cell as in FIG. 2. The cell had a time averaged running voltageof about 0.71 volts. The capacity obtained at this cut off voltage was226 milliAmp-hrs. The specific capacity of the copper hydroxide was1,237 milliAmp per cubic centimeter total cathode volume (532milliAmp-hours per gram copper hydroxide). The energy output of the cellwas 160 milliWatt-hrs. The cathode 170 had a resistivity of 0.55ohm-meters.

EXAMPLE 4B Zn Anode: Copper Hydroxide Cathode with Expanded Graphite

Test cell 110 was prepared as in example 3B except that the cathode 170was formed of the following cathode mixture embodiment comprising a lessresistive copper hydroxide Cu(OH)₂. Graphite material in the form ofexpanded graphite was added as in Example 3B. The cathode 170 had 0.42grams of copper hydroxide and was balanced with zinc in anode 150 inexcess as above described. The cathode 170 had the followingcomposition:

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 Expanded graphite²7.0 9.0 (WH20) KOH aqueous 8.3 17.5 Solution (38 wt. % KOH and 2 wt. %ZnO) Polyethylene 0.5 1.30 Binder 100.0 100.0 Notes: ¹The wt. % valueshave been converted from vol. % using the following real densities:Cu(OH)₂, 3.37 g/cc; expanded graphite, (2.25 g/cc); and 38 wt. % KOHaqueous solution (1.37 g/cc); polyethylene binder, 1.0. The Cu(OH)₂ waslower resistive copper hydroxide from Alfa Aesar Company, stock #32733(assay 94 wt. % purity copper hydroxide). ²Expanded graphite WH20 fromChuetsu Company.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm², approximately equal to a constant currentdischarge of about 250 milliAmp in a AA size cell as in FIG. 2. The cellhad a time averaged running voltage of about 0.70 volts. The capacityobtained at the above cut off voltage was 229 milliAmp-hrs. The specificcapacity of the copper hydroxide was 1262 milliAmp-hours per cubiccentimeter total cathode volume (535 milliAmp-hours per gram copperhydroxide). The energy output of the cell was 160 milliWatt-hrs. Thecathode 170 had a resistivity of 0.11 ohm-meters.

EXAMPLE 4C Zn Anode; Copper Hydroxide Cathode with Graphitic CarbonNanofibers

Test cell 110 was prepared as in Example 3C except that the cathode 170is formed of the following cathode mixture embodiment comprising a lessresisitve copper hydroxide Cu(OH)₂. The graphite material in the form ofgraphitic carbon nanofibers was added as in Example 3C. The cathode 170had 0.42 grams of copper hydroxide and was balanced with zinc in anode150 as above described. Cathode 170 had the following composition:

Cathode Composition¹ Wt. % Vol. % Cu(OH)₂ 84.2 72.2 carbon nanofiber²7.0 9.0 (PR19HT from Applied Sciences) KOH aqueous 8.3 17.5 Solution (38wt % KOH and 2 wt. % ZnO) Polyethylene Binder 0.5 1.3 100.0 100.0 Notes:¹The wt. % values have been converted from vol. % using the followingreal densities: Cu(OH)₂, 3.37 g/cc; graphitic carbon nanofiber, (2.25g/cc); and 38 wt. % KOH aqueous solution (1.38 g/cc). The Cu(OH)₂ waslower resistive copper hydroxide from Alfa Aesar Company, stock #32733(assay 94 wt % purity copper hydroxide). ²Graphitic carbon nanofiberfrom Applied Sciences, Cedarville, Ohio, post heat treated attemperatures between about 2500° C. and 3100° C. The fibers had anaverage diameter of 200 nanometer and average length of 200 micron.

The cell 110 was discharged at a constant rate of 22 milliAmp to a cutoff voltage of 0.1 volts. This is equivalent to a current density ofabout 21 milliAmp/cm² based on the anode/cathode interface,approximately equivalent to a current drain of about 250 milliAmp in anAA size cell as in FIG. 2. The cell had a time averaged running voltageof about 0.75 Volts. The capacity obtained at the above cut off voltagewas 219 milliAmp-hrs. The specific capacity of the copper hydroxide was787 milliAmp-hours per cubic centimeter total cathode volume (523milliAmp-hours per gram copper hydroxide). The energy output of the cellwas 165 milliWatt-hrs. The cathode 170 had a resistivity of 0.038ohm-meters.

The cell performance of Examples 4A-4C is summarized in the Table 4.

TABLE 1 Percent Capacity Reduction mAmp-hr in resistivity @ 22 mAmpCathode versus (Ex. 1A) discharge resistivity cathode with AverageRunning rate to 0.1 V Energy Output, Cathode ohm-meter natural graphiteVoltage (Volts) cut off mWatt-hour Ex. 1A 0.335 0.91 161 147 EMD andnatural graphite (NdG15) Ex. 1B 0.075 77.6 1.01 156 158 EMD and expandedgraphite (WH20) Ex. 1C 0.022 93.4 1.01 155 157 EMD and carbon nanofibers(PR19HT) Notes: 1. The cathode mixtures were all at 72.2 vol % EMDactive material with included aqueous KOH electrolyte as specified inthe respective examples.

TABLE 2 Percent Capacity Reduction mAmp-hr in resistivity @ 22 mAmpCathode versus (Ex. 2A) discharge resistivity cathode with AverageRunning rate to 0.1 V Energy Output, Cathode ohm-meter natural graphiteVoltage (Volts) cut off mWatt-hour Ex. 2A 0.344 0.74 506 373 CuO andnatural graphite (NdG15) Ex. 2B 0.054 84.3 0.74 518 381 CuO and expandedgraphite (WH20) Ex. 2C 0.054 84.3 0.75 518 383 CuO and carbon nanofibers(PR19HT) Notes: 1. The cathode mixtures were all at 72.2 vol % CuOactive material with included aqueous KOH electrolyte as specified inthe respective examples. 2. The CuO was ACS (American Chemical Society)grade at 99.5 wt. % purity obtained from Fisher Scientific Company.

TABLE 3 Percent Capacity Reduction mAmp-hr in resistivity @ 22 mAmpCathode versus (Ex. 3A) discharge resistivity cathode with AverageRunning rate to 0.1 V Energy Output, Cathode ohm-meter natural graphiteVoltage (Volts) cut off mWatt-hour Ex. 3A 234 0.64 212 136 Cu(OH)₂ andnatural graphite (NdG15) Ex. 3B 2.6 98.9 0.62 204 126 Cu(OH)₂ andexpanded graphite (WH20) Ex. 3C 1.03 99.6 0.62 209 130 Cu(OH)₂ EMD andcarbon nanofibers (PR19HT) Notes: 1. The cathode mixtures were all at72.2 vol % Cu(OH)₂ active material with included aqueous KOH electrolyteas specified in the respective examples. The Cu(OH)₂ was resistivecopper hydroxide from Aldrich Chemical Co., Inc. Catalog #28,978.7(assay less than 92 wt. % copper hydroxide).

TABLE 4 Percent Capacity Reduction mAmp-hr in resistivity @ 22 mAmpCathode versus (Ex. 3A) discharge resistivity cathode with AverageRunning rate to 0.1 V Energy Output, Cathode ohm-meter natural graphiteVoltage (Volts) cut off mWatt-hour Ex. 4A 0.55 0.71 226 160 Cu(OH)₂ andnatural graphite (NdG15) Ex. 4B 0.11 80.0 0.70 229 160 Cu(OH)₂ andexpanded graphite (WH20) Ex. 4C 0.038 93.1 0.75 219 165 Cu(OH)₂ EMD andcarbon nanofibers (PR19HT) Notes: 1. The cathode mixtures were all at72.2 vol % Cu(OH)₂ active material with included aqueous KOH electrolyteas specified in the respective examples. The Cu(OH)₂ was lower resistivecopper hydroxide from Alfa Aesar Company, stock #32733 (assay 94 wt %purity copper hydroxide).

The average running voltage for examples 2A-2C (Table 2) employingcopper oxide cathode or examples 3A-4C (Tables 3 and 4) comprisingcopper hydroxide cathode is somewhat lower than corresponding examples1A-1C utilizing manganese dioxide cathode.

Table 1 shows lowering of cathode resistivity and some improvement inenergy output when natural graphite is replaced with expanded graphiteor graphitic carbon nanofibers in alkaline cell cathode comprisingelectrolytic MnO₂ (EMD).

Table 2 shows lowering of cathode resistivity when natural graphite isreplaced with expanded graphite or graphitic carbon nanofibers inalkaline cell cathodes comprising copper oxide. The capacity is higherin each example summarized in Table 2 when compared to the MnO₂ cathodesreported in Table 1.

Table 3 shows very significant lowering of cathode when natural graphiteis replaced with expanded graphite or graphitic carbon nanofibers inalkaline cell cathodes comprising highly resistant copper hydroxide. Thelowering of cathode resistivity is more pronounced when graphitic carbonnanofibers is employed. The capacity is higher (energy output somewhatlower) in each example in Table 3 when compared to the MnO₂ cathodesreported in Table 1.

Table 4 also shows very significant lowering of cathode resistivity whennatural graphite is replaced with expanded graphite or graphitic carbonnanofibers in alkaline cell cathodes comprising less resistive copperhydroxide. The lowering of cathode resistivity is more pronounced whengraphitic carbon nanofibers is employed. The capacity is higher in eachexample in Table 4 when compared to the MnO₂ cathodes reported in Table1.

The dramatic lowering of cathode resistivity achieved in alkaline cellcopper oxide or copper hydroxide cathodes achieved when natural graphiteis replaced with expanded graphite or graphitic carbon nanofbiers,particularly the latter, is very significant. The dramatic lowering ofthe cathode resistivity in such cells is expected to result in moresignificant performance improvement when the copper oxide or copperhydroxide alkaline cells with thicker cathodes (e.g. AA, C and D cells)are compared to the same cells with MnO₂ cathodes. Also, the achievementof significant lowering of cathode resistivity in copper oxide andcopper hydroxide alkaline cells as herein reported sets the stage forfurther improvement of these cells by including additional cathodeadditives, for example, titanium compounds and the like.

Although the invention has been described with respect to specificembodiments, it will be appreciated that variations are possible withinthe concept of the invention. Thus, the invention is not intended to belimited to the specific embodiments herein described, but is betterdefined by the claims and equivalents thereof.

1. An electrochemical cell comprising an anode comprising anode activematerial, an aqueous alkaline electrolyte solution, a separator, and acathode comprising copper oxide and carbon nanofibers.
 2. The cell ofclaim 1 wherein the cathode comprises copper oxide and a portion of saidaqueous alkaline solution.
 3. The cell of claim 1 wherein the anodeactive material comprises zinc.
 4. The cell of claim 1 wherein theelectrolyte solution comprises potassium hydroxide.
 5. The cell of claim1 wherein the carbon nanofibers have a diameter less than 500nanometers.
 6. The cell of claim 1 wherein said carbon nanofibers have amean average diameter between about 50 and 300 nanometers.
 7. The cellof claim 1 wherein said carbon nanofibers have a mean average lengthbetween about 0.5 and 300 micron.
 8. The cell of claim 1 wherein saidcarbon nanofiber comprises less than 200 million parts by weight metalper million parts carbon.
 9. The cell of claim 1 wherein said carbonnanofibers comprises between about 4 and 10 percent by weight of thecathode.
 10. The cell of claim 1 wherein said carbon nanofiberscomprises graphitic carbon nanofibers.
 11. The cell of claim 1 whereinsaid copper oxide has a purity of at least 97.0 percent by weight. 12.The cell of claim 1 wherein said copper oxide has a purity of between97.0 and 99.8 percent by weight.
 13. The cell of claim 1 wherein thecathode comprises between about 80 and 92 percent by weight copperoxide.
 14. The cell of claim 1 wherein the copper oxide is inparticulate form having an average particle size between about 1 and 100micron.
 15. The cell of claim 1 wherein said cell comprises less than 50parts by weight mercury per million parts total cell weight.
 16. Anelectrochemical cell comprising an anode comprising anode activematerial, an aqueous alkaline electrolyte solution, a separator, and acathode comprising copper oxide and expanded graphite.
 17. The cell ofclaim 16 wherein the cathode comprises copper oxide and a portion ofsaid aqueous alkaline solution.
 18. The cell of claim 16 wherein theanode active material comprises zinc.
 19. The cell of claim 16 whereinthe electrolyte solution comprises potassium hydroxide.
 20. The cell ofclaim 16 wherein said expanded graphite comprises between about 4 and 10percent by weight of the cathode.
 21. The cell of claim 16 wherein saidcopper oxide has a purity of at least 97.0 percent by weight.
 22. Thecell of claim 16 wherein said copper oxide has a purity of between 97.0and 99.8 percent by weight.
 23. The cell of claim 16 wherein the cathodecomprises between about 80 and 92 percent by weight copper oxide. 24.The cell of claim 16 wherein the copper oxide is in particulate formhaving an average particle size between about 1 and 100 micron.
 25. Thecell of claim 16 wherein said cell comprises less than 50 parts byweight mercury per million parts total cell weight.
 26. Anelectrochemical cell capable of producing electrical energy comprisingan anode comprising zinc anode active material, an aqueous alkalineelectrolyte solution comprising potassium hydroxide, a separator, and acathode comprising copper hydroxide and graphitic carbon selected fromthe group consisting of graphitic carbon nanofibers and expandedgraphite, and mixtures thereof.
 27. The cell of claim 26 wherein thecathode comprises copper hydroxide and a portion of said aqueousalkaline solution.
 28. The cell of claim 26 wherein the graphitic carboncomprises between about 4 and 10 percent by weight of the cathode. 29.The cell of claim 26 wherein said graphitic carbon nanofibers have adiameter less than 500 nanometers.
 30. The cell of claim 29 wherein saidcarbon nanofibers have a mean average diameter between about 50 and 300nanometers.
 31. The cell of claim 29 wherein said carbon nanofibers havea mean average length between about 0.5 and 300 micron.
 32. The cell ofclaim 29 wherein said carbon nanofibers comprise less than 200 parts byweight metal per million parts carbon.
 33. The cell of claim 29 whereinsaid carbon nanofibers comprises between about 4 and 10 percent byweight of the cathode.
 34. The cell of claim 26 wherein the cathodecomprises between about 80 and 92 percent by weight copper hydroxide.35. The cell of claim 26 wherein said cell comprises less than 50 partsby weight mercury per million parts total cell weight.